The invention relates to blood collection systems particularly, but not exclusively, those of the type comprising an evacuated blood-collection tube closed by a stopper and an open, tubular double-ended needle holder slidably mounted on the tube or its stopper. This needle holder carries a hollow needle having one part protruding axially from the closed end of the holder, for pricking into a vein, and another part extending axially within the holder, the latter part being encased in a loose, flexible cover or sleeve. To take a blood sample, the needle is pricked into a vein and the evacuated tube displaced until the needle pierces the stopper membrane, so that blood is sucked into the evacuated tube.
However, in practice, conventional evacuated blood sampling systems are often difficult to use or have shortcomings that create health hazards for laboratory staff and may alter the results of some blood determinations. This is particularly the case with samples collected for determinations of the blood sedimentation rate, using standardized sedimentation pipettes known as the Westergren or the Wintrobe types. The Westergren is characterized by a narrow, 2.5 bore, an outer diameter of 5.5 mm and a length of 25 to 27 mm. Filled with blood and placed on a rack, they allow reading of the rate of sedimentation of blood cells for a given sample of blood.
The difficulty stems mainly from the need to open the collection tube in order to introduce the sedimentation pipette in it and to transfer the sample either by sucking it (mouth pipetting) or by mechanical means, such as electric pumps.
New devices have been proposed with a cylindrical washer or plunger set at one end of the pipette. These pipettes are introduced into the collection tube after opening, the peripheral wall of the plunger sliding tightly against the inner wall of the tube. The pipette is lodged in a central bore in the plunger. At the bottom end of the plunger is a type of slotted membrane which acts as a valve so that when the pipette is pushed down the collection tube, blood raises into its bore up to a determined level.
All these devices have in common the drawback of necessitating opening of the collection tube. This creates concern to the laboratory staff as the blood samples with which such determinations are made have a higher than the average contamination risk, e.g. viral hepatitis.
Furthermore with the above mentioned pipettes having a cylindrical plunger, there is a risk of air bubbles forming in or being transferred into the pipettes, with possible alteration of the results. Owing to this factor, their handling calls for rather careful and lengthy operations, not appropriate when a high number of tests is involved.
Another shortcoming of evacuated tubes is the well known fact that due to the vacuum in the tubes, blood gushes out of the needle in a narrow parallel jet with an exagerated speed and strength, breaking against the tube inner wall and entailing an alteration of the blood cells which may affect certain determinations, among which coagulation and sedimentation rates are the most vulnerable ones.